A. Technical Field
The present invention relates to fluid disinfection and ultraviolet (UV) disinfection devices, and more particularly, to fluid disinfection apparatus having submersible UV radiation disinfection devices.
B. Background of the Invention
Water and other liquids may carry infectious pathogenic microorganisms, such as bacteria, spores, viruses, and fungi, that need to be disinfected/sterilized to protect public health. UV light is known to have germicidal properties and has been developed as the disinfection light source. Specifically, the mechanism by which UV light kills microorganisms is by damaging the genetic material, the deoxyribonucleic acid (DNA), of the microorganisms and wavelengths between 200-300 nm have been shown to initiate a photoreaction between adjacent pyrimidines.
In general, different microbes have different UV disinfection dosages. When using the conventional low-pressure mercury lamp UV emissions at 254 nm, the National Sanitation Foundation (NSF) Standard 55-1991 Ultraviolet Microbiological Water Treatment Systems demand the NSF failsafe set-point dosage for Class A systems UV water treatment system is 40 mJ/cm2, and International Water-Guard designs its Class A units to operate at a minimum dosage of 40 mJ/cm2 as well. Class A systems are those designed to disinfect water contaminated by micro-organisms like bacteria and viruses, but not water with an obvious contamination source such as raw sewage, nor are they designed to convert wastewater to safe drinking water. Class B systems are intended to provide supplemental treatment of drinking water that has been tested by health authorities and deemed acceptable for human consumption. The NSF dosage requirement for Class B systems using 254 nm emission is 16 mJ/cm2. Use of 265-275 nm UV emissions for disinfection, which have the maximal UV germicidal effect, can reduce the required dosage for the same germicidal effect as compared to the use of 254 nm UV light. UV emissions at 265 nm and in the range of 200 nm to 400 nm can be generated by group III nitride semiconductor UV light emitting diodes (LEDs).
To design an efficient UV disinfection apparatus for fluids and liquids with targeted UV dosage, various aspects have to be taken into consideration. Firstly, UV radiations can only penetrate a liquid to a certain depth, and as such, any liquid that is farther away from the radiation source than the penetration depth is not sufficiently irradiated. Secondly, UV radiation or UV light can be readily absorbed by fluid container's surface, since most solids have very small UV reflectivity. This requires optical designs to minimize UV/container encounter. Thirdly, UV dosage delivered is proportionally to UV exposure duration time. An efficient design thus will maximize UV duration time, without merely relying on increasing UV light source output power. Thus, there is a need for fluid disinfection apparatuses having submersible UV light devices that address the above identified considerations.